John Deere 2520 no charge pump pressure

[Oregon2023]

I went through again and applied compressed air to all of the oil passages in the valve block and found the forward directional control valve was leaking. I removed and cleaned it and reinstalled. When I applied compressed air again there was no leak. The charge pump directly feeds pressurized oil to this valve. I’m betting money this was the problem all along, and the directional control valves can be removed from the top of the valve block without splitting the tractor.

 

[oldnslo]

Oregon
Excellent troubleshooting and I hope that was your problem.

A question before you start reassembly. Do you have a detailed schematic showing the charge pump flow path? I suspect PTO is first function, then steering, then HST charge circuit. Would the leaking valve prevent pressure build up in all these circuits.

The info on post 7 kind of describes flow path and is what makes me question if that valve would prevent steering.

 

[Oregon2023]

Oregon
Excellent troubleshooting and I hope that was your problem.

A question before you start reassembly. Do you have a detailed schematic showing the charge pump flow path? I suspect PTO is first function, then steering, then HST charge circuit. Would the leaking valve prevent pressure build up in all these circuits.

The info on post 7 kind of describes flow path and is what makes me question if that valve would prevent steering.

Yes, I have the John Deere service manual for this model.

The PTO and steering have much smaller valves and wouldn't work if the larger directional control valves are stuck open leaking out all of the charge pump's pressure.

 

[Oregon2023]

I finally found the problem. The shaft that broke going into the transmission had pushed on the main hydrostatic pump block causing it to sit at a slight angle scoring the valve plate resulting in an excessive gap that created a massive internal loss of pressure. Reinstalled a new hydrostatic pump and valve plate and works as good as new now.

 

[oldnslo]

Glad you have it repaired and back in operation.

 

[Hoss710]

How much was the wear to cause such a problem? a few thousands? or was it way more than that ?